The invention relates generally to cable television descramblers, and deals more particularly with a low cost descrambler system which does not appreciably degrade nonscrambled channels transmitted simultaneously with the scrambled channel.
Heretofore, a broadband cable television (CATV) signal was supplied to a power splitter at the input of a descrambler system. A band reject filter was coupled to one output of the power splitter to reject the scrambled channel. A descrambler was coupled to another output of the power splitter to descramble the scrambled channel. The outputs of the band reject filter and the descrambler were combined and transmitted to a television or other video appliance, which output contained the descrambled channel as well as other nonscrambled channels.
One problem with such a descrambler system is that all the nonscrambled channels must pass through the band reject filter, and this filter degrades to various degrees the nonscrambled channels, especially the channels adjacent to the scrambled channel. Also, the band reject filter is expensive because it is sharp; the filter typically provides 60 decibels of attenuation of the scrambled channel. Moreover, such a system includes up and down converters in the descrambler to convert the frequency of the scrambled channel to the frequency of the bandpass filter.
Accordingly, a general object of the present invention is to provide a low cost descrambler system which does not appreciably interfere with nonscrambled channels yet provides effective descrambling.
A more specific object of the present invention is to provide a descrambler system of the foregoing type which does not require a filter to pass nonscrambled channels, or up and down converters for converting the frequency of the scrambled channel to an unused channel.
Another ancillary object of the present invention is to provide descrambler systems of the foregoing type which can be installed either as off-premise or on-premise devices.